Unio downiei Lea, 1858
Lea, 1858. Proc. Acad. Nat. Sci. 10: 166.
Lea, 1859. Jour. Acad. Nat. Sci. 4 [O. 7]: 210 [28], pl. 25, fig. 91.
Type(s): HOLOTYPE USNM_84854, Satilla R., Ga.

Unio (sec. Elliptio) downiei — Simpson (1900), Simpson (1914)
— de Gregorio (1914)
Elliptio (s.s.) downiei — Frierson (1927), Haas (1969)
Elliptio (s.s.) crassidens downiei — R.I. Johnson (1970)
Elliptio downiei — Turgeon et al. (1988), Williams et al. (1993), Turgeon et al. (1998), Graf & Cummings (2007), Bogan (2010), ... Williams et al. (2017), Graf & Cummings (2021), FMCS (2021), Hopper et al. (2023), MolluscaBase (2024)

Unio satillaensis Lea, 1858
Lea, 1858. Proc. Acad. Nat. Sci. 10: 166.
Lea, 1859. Jour. Acad. Nat. Sci. 4 [O. 7]: 216 [34], pl. 27, fig. 96.
Type(s): HOLOTYPE USNM_84855, Satilla R., Camden Co., Ga.

Unio (sec. Elliptio) geminus — Simpson (1900), Simpson (1914)
Elliptio (s.s.) geminus — Frierson (1927), Haas (1969)
Elliptio (s.s.) crassidens downiei — R.I. Johnson (1970)
Elliptio (s.s.) crassidens — Burch (1975)

Unio spissus Lea, 1859
Lea, 1859. Proc. Acad. Nat. Sci. 11: 112.
Lea, 1859. Jour. Acad. Nat. Sci. 4 [O. 7]: 208 [26], pl. 25, fig. 89.
Type(s): HOLOTYPE USNM_84853, Satilla R., Ga.

Unio (sec. Elliptio) spissus — Simpson (1900), Simpson (1914)
Elliptio (s.s.) spissus — Frierson (1927), Haas (1969)
Elliptio (s.s.) crassidens downiei — R.I. Johnson (1970)
Elliptio (s.s.) crassidens — Burch (1975)

Unio downei Sowerby, 1868
‘Lea’ Sowerby, 1868. Conch. Icon. 16: pl. 68, sp. 350.
(error for Unio downiei Lea, 1858)

Unio (sec. Elliptio) downiei — Simpson (1900)

Unio dowiei de Gregorio, 1914
‘Lea’ de Gregorio, 1914. Il Nat. Siciliano 2: 54.
(error for Unio downiei Lea, 1858)